In your /etc/rc.d folder, do you have rc.wireless and rc.wireless.conf? I can tell you how I got my wireless to work at boot.
In my rc.wireless.conf, there's a section at the top that says
## Pick up any Access Point, should work on most 802.11 cards
So, if you have that file, I would set your ESSID there. Can't remember what INFO does, but you might just want to set it to the same as your ESSID.
Then, in rc.local, I have added the following two lines:
HTH. By the way, I got that stuff from here
(even though my card isn't a Linksys, I just had to edit accordingly).